Upper bound supported PHP version in README

Author: GrahamCampbell

README.md

@@ -32,7 +32,7 @@ Happy browsing!
 Requirements
 ------------
 
-Requires PHP 7.1+ and a chrome/chromium 65+ executable.
+Requires PHP 7.1-8.0 and a chrome/chromium 65+ executable.
 
 Note that the library is only tested on Linux but is compatible with MacOS and Windows.